1. Field of the Invention
This invention relates to a door closer adapted to gradually close a door by employing a high polymer viscous liquid such as polyisobutyne, etc., or other high viscosity liquid and a return spring, automatically closing the door by the accumulated recovering force of the spring and generating a braking force at the door by the resistance force of the high viscous liquid.
2. Description of the Prior Art
A conventional door closer which consists of a hydraulic cylinder provided in a body case of a laterally long shape, a piston telescopically inserted into the hydraulic cylinder through a return spring, a rack engraved on one sidewall of the piston, and a pinion rotatably supported to a pinion shaft to be engaged with the rack at one side of the cylinder is well known.
In the door closer of the arrangement described above, the body case is fixed to the door and a link pivotally secured at one end thereof to be rotatable to the end of an arm fixed to the pinion shaft is provided at the other end thereof with a mounting bracket to be rotatable, and the mounting bracket is fixed to an upper frame. Thus, the door closer is mounted at the door. The piston is moved against the return spring by the pinion at the time of opening the door, and the door is automatically closed by the accumulated recovering force of the return spring at the time of closing the door.
Cutout toothed portions are formed at the rack and the portion of the pinion in the door closer. Thus, the door becomes in a free state in a range from a predetermined door opening angle to a door fully opening angle, and the door can be freely opened and closed, or locked. Further, the teeth of both ends of the rack and the pinion are engaged with each other to lock the door at a predetermined opening angle.
However, in the door closer of the arrangement described above, the piston has power transmission means to be driven by the pinion meshed with the rack formed on one sidewall of the piston. Therefore, there arise various problems as will be described below. Bearings for rotatably supporting the pinion shaft to the body case are relatively quickly worn due to the thrust load of the pinion shaft. When power is transmitted to the piston through the rack of one side, a bending load is applied to the piston in its moving direction. Thus, the piston and the cylinder are irregularly worn. When the door is locked at a predetermined door opening angle or the lock of the door is released, an unpleasant vibration noise is generated due to the forcible disengagement or engagement of both the end teeth of the rack and the pinion. Or, both the end teeth of the rack and the pinion are easily damaged due to the collision of the rack and the pinion when the door is abruptly opened or closed by a strong force or when the door is acted on by strong wind in the closing direction at the locked position of a predetermined door opening angle.